This invention relates broadly to electronic load-monitoring devices and more particularly to an improved adjustable-range electronic relay for giving warning when the current flow through a motor or other electrical load varies from a preselected operating range.
Mechanical alarm relays commonly are employed to monitor current flow through an electrical load and to energize alarm circuitry when the monitored current increases to a preselected high value or decreases to a preselected low value. The relay is provided with mechanical contacts for operating the alarm circuitry. It is typical for such relays to include a mechanical adjustment permitting re-setting of the high and low current values at which the relay alarms--that is, the relays are designed for mechanical adjustment of the alarm range.
Mechanical relays of the kind just described are characterized by various disadvantages. Being mechanical devices, the relays do not provide as high an alarm point accuracy and repeatability as would be desired. Also, such relays require various mechanical adjustments. Again, the relay contacts are often slow-acting and thus subject to arcing and chattering.